Dr. Barbara Clark was selected for career initiation support by the Research Development Core Advisory Committee for her proposal "Hormonal Regulation of Extracellular Fluid Volume in the Old." Dr. Clark is a trainee in the Physician Scientist Training Program entering Phase II, or the early stage of independent investigation and has developed a parallel set of investigations to her primary interest in the physiology of renal sodium excretion. Support for the proposed two years of pharmacologic study of ANP in the elderly will broaden Dr. Clark's systematic examination of renal physiology and aging. Dr. Clark will continue to work with her mentor, Dr. Franklin Epstein, Chief of Nephrology at the Beth Israel Hospital, examining the hypothesis that 1) aging is associated with altered release of ANP in response to volume stimuli, 2) age-related elevation of ANP levels seen in aging are associated with end organ renal and vascular resistance, 3) elevated ANP levels seen with age may be responsible for lower basal vasopressin levels and 4) aging is associated with increased susceptibility for hyponatremia. The proposed studies, conducted largely in the Beth Israel Hospital Clinical Research Center will be supervised by Dr. Franklin Epstein, an internationally respected Academic Nephrologist and Professor of Medicine at Harvard Medical School. The RIA, Subject Recruitment, and the Physiology Cores will be necessary components of Dr. Clark's research support.